Equation domain elements

The elements in the equation domain enable authors to clearly distinguish equations
from other type of content. These markup distinctions can enable formatting distinctions,
numbering of equations, and more. This domain can be used independently of the MathML domain.

The equation domain elements do not attempt to satisfy all possible requirements for
representing equations semantically. More sophisticated users of equations might need to
further specialize from these elements or provide an alternative vocabulary for semantic
equations.